Histopathologic study of veins in steroid treated rabbits.

Although arterial factors have been regarded as playing an important role in the pathogenesis of osteonecrosis, more attention has been given to venous factors because steroids cause an increase in the intraosseous pressure despite a decrease in blood flow in the femoral head. The authors examined changes in the veins of steroid treated rabbits. Forty rabbits were used: 30 rabbits (the steroid treated group) were injected with methylprednisolone acetate (4 mg/kg) weekly and 10 rabbits (the control group) were treated without steroids. The veins around the femoral head, ear veins, femoral veins, and inferior vena cava were obtained after 8 weeks of treatment, and the specimens were examined by immunohistochemical staining and electron microscopy. In the steroid treated group, proliferation of foam cells was observed in the intima of the vein in 7 of 30 rabbits. Immunohistochemical studies, using monoclonal antibodies for smooth muscle cells and macrophages, showed that the foam cells were derived from smooth muscle cells. Electron microscopy showed damage to the endothelial cells and smooth muscle cells. These results indicated that corticosteroids damaged the venous system. It is suggested that steroid induced disturbance of the draining veins causes stasis and that steroids are an important factor in osteonecrosis of the femoral head.